1. Field of the Invention
The present invention relates, in general, to a method for manufacturing a p-type GaN-based thin film using plasma nitridation together with rapid thermal annealing (hereinafter referred to as "RTA"), thereby providing high hole concentration for the thin film. Formation of p-type GaN-based thin films with high hole concentration is one of the most essential techniques in fabricating optoelectronic devices such as blue/white light emitting diodes (LEDs), laser diodes (LDs) and electronic devices which employ nitride semiconductors.
2. Description of the Prior Art
Reliable formation of high conductivity p-type GaN is one of the most demanding techniques in fabricating optoelectronic devices such as blue-green light emitting diodes (LEDs), blue laser diodes (LDs), and solar-blind ultraviolet photodetectors. For Mg-doped GaN grown by metalorganic chemical vapor deposition (MOCVD), however, it was difficult to obtain p-type conductivity due to the passivation by electrically inactive Mg--H complexes which are formed in the films by hydrogen from the growth ambient. To overcome this problem, a low energy electron beam irradiation [H. Amano el al., Jpn. J. Appl. Phys. 28, L2112 (1989)] or a RTA at 700.degree. C. for 20 min in an N.sub.2 ambient [S. Nakamura et al., Jpn. J. Appl. Phys. 31, L139 (1992)] has been commonly employed to dissociate hydrogen from the Mg--H complexes, giving rise to a p conduction with hole density in the low 10.sup.17 cm.sup.-3 range. Currently, RTA dominates over other treatments in activating the Mg acceptors. The problem has been intensified by the presence of compensating donor defects, e.g., the nitrogen vacancy whose formation is energetically favorable under p-type conditions. To date, the activation of the Mg acceptors in GaN thin films grown by a MOCVD process has been utterly dependent on such thermal treatments. However, the self-compensation can not be mastered by the post growth treatments and remains to be overcome to achieve hole concentration above mid-10.sup.17 cm.sup.-3. In this regard, a new technique to further improve the p-conductivity is highly desired in the GaN-based III-nitride thin films.